HVAC Control and Direct Digital Controls 2 - An HVAC technician who knows nothing about HVAC control systems would wonder how these HVAC control systems work. To understand HVAC controls, one must understand basic electricity and circuits.
DDC Control Module for an Air Handling Unit – This is a direct digital controls control module for an air handler that serves some VAV boxes in office spaces for a Data Center. This DDC control module includes analog and digital inputs and analog and digital outputs to handle all the control functions necessary to control the devices and components on a large commercial air handler. (more…)Hydronic Pump Cavitation - Pump cavitation can cause severe problems to a pump if not addressed and corrected. To understand the cause of cavitation you need to understand the pressure-temperature relationship of the liquid in the loop. Whether it is water or water/glycol mix. As the water passes through the pump it changes the pressure from the suction side to the discharge side of the pump.
If the water’s static pressure drops too much vapor is created causing tiny bubbles in the water or fluid in the loop passing through the pump. These bubbles are unstable and collapse causing severe turbulence inside the bearing assembly and can damage the impeller. (more…)
DDC Integration | HVAC DDC Controls - This is an electrical project which is in the process of changing the old control system to a new DDC control system. Installing new controls in an occupied building takes plenty of planning to avoid interruption in air conditioning or heating. The old control system was a basic electro-mechanical control system which little more than just basic building management control.
Magnehelic Duct Pressure Sensor - The Magnehelic measures duct pressure inside of ductwork. It is important, for many reasons, to know the pressure inside of ductwork. This Magnehelic measures the supply side pressure of the blower inside the air handler. (more…)
In HVAC a variable speed drive is a speed control system for electric motors. The variable speed drive (VSD) or variable frequency drive (VFD), among other names (adjustable-frequency drives (AFD), AC drives, micro-drives, or inverter drives). The application of variable speed drives has brought about a new way of engineering buildings and control systems HVAC.
The flow of water and air can now be regulated precisely using VSD’s and state-of-the-art control systems. By combining VSD’s with state-of-the-art control systems, large savings in energy usage can see realization because the exact quantity of flow of water or air can be delivered to satisfy demand.
Demand-based control is energy efficient. VSD’s can be stand-alone or controlled by a building automation system.
DDC Programming Logic 3 - DDC control logic blocks have practically an unlimited way of arranging the blocks for HVAC control. Below is an example of a line of logic blocks arranged for static pressure control of a VAV air handler supply fan using a variable frequency drive. This same arrangement could also be used for static pressure control using a bypass damper instead of a VFD. (more…)
Programming DDC Logic 2 - The analog network input is similar to an analog input except this input is not hardwired to the local controller but on a remote controller in the network. It is very important that the communication works effectively for this analog network input to work. An example of this is the outside air temperature which is hardwired to a DDC controller in the penthouse of a multistory building.
The building engineer only wants the boilers to fire if the outside air temperature is less than 55° F. Instead of having an outside air temperature device hardwired to the boiler controller an analog network input can be placed into the boiler controller program and linked to the outside air temperature reading which is in the penthouse controller where the outside air temperature thermistor is hardwired. This saves devices and wires necessary for optimum control.
Air Handler Filter Pressure Sensor - This is a pressure sensor. It tells a maintenance technician if the air filters are dirty and clogged. The pressure control is a low static pressure switch to trip the unit if the mixing box drops below the setpoint pressure. The pressure the switch is calibrated to.
In addition, the low static pressure sensor protects the fan and the ductwork including dampers from damage. If the economizer damper and the return air damper would fail closed (or another possible scenario) that would cause the unit to pull negative pressure in the mixing box. (more…)
These Alerton controllers control a heat exchanger and air handler
Alerton Controllers DDC HVAC Control - HVAC DDC control has become an integral part of building automation systems. Modern DDC HVAC Control is a state-of-the-art computer-controlled system that adds efficiency to the system. These Alerton controllers are used to monitor and control an air handling unit for a large building. (more…)
